Epitaxial polymerization of (SN)x: Chemical defects

Abstract

Epitaxially polymerized (SN)_x on various substrates has been studied by Fourier‐transform infrared spectroscopy (FT‐ir). Those substrates include Pt‐shadowed KI, AgCl, NaCl, KCl, KI, KBr, RbI, and NaI. All samples of the polymer contained significant amounts of chemical defects, mostly as NH and S=O groups. The spectral variation observed with (SN)_x polymerized on various substrates appeared to be due to differences in its degradation by water. There are at least two distinct degradation mechanisms. One is the degradation by water incorporated into the S₂N₂ crystals prior to the polymerization, and the other is the attack of moisture on the polymer. The nature of the chemical defects were studied by deuterium exchange and degradation by H₂ ¹⁸O as well as H₂ ¹⁶O. The band at 1400 cm⁻¹ was assigned to the NH group while two bands at 1220 and 1090 cm⁻¹ were assigned to S=O groups with different chemical environments. The band at 1220 cm⁻¹ is related to a structure produced during the early stages of degradation in the preparative vacuum chamber, but the band at 1090 cm⁻¹ is thought to arise from a structure formed at a later stage of degradation after sample preparation by atmospheric water.